Why does the C++ standard algorithm “count” return a difference_type instead of size_t?

by

The std::count() algorithm relies on the iterator type to define an integral type large enough to represent any size of a range. Possible implementation of containers include files and network streams, etc. There is no guarantee that the entire range fits into the process’ address space at once, so std::size_t might be too small.

The only integral type offered by the standard std::iterator_traits<> is std::iterator_traits<>::difference_type, which is suitable for representing “distances” between two iterators. For iterators implemented as (wrappers of) pointers, this type is std::ptrdiff_t. There is no size_type or the like from iterator traits, so there is no other choice.

More Related Contents:

  1. Replace part of a string with another string
  2. What is the performance overhead of std::function?
  3. How to create an std::function from a move-capturing lambda expression?
  4. A std::map that keep track of the order of insertion?
  5. Is std::vector or boost::vector thread safe?
  6. How is std::string implemented?
  7. How to get error message when ifstream open fails
  8. Why is the destructor of a future returned from `std::async` blocking?
  9. Should I use std::function or a function pointer in C++?
  10. Append an int to a std::string [duplicate]
  11. When using C headers in C++, should we use functions from std:: or the global namespace?
  12. declaring a priority_queue in c++ with a custom comparator
  13. How std::bind works with member functions
  14. Can std::begin work with array parameters and if so, how?
  15. do I need to close a std::fstream? [duplicate]
  16. C++ Add months to chrono::system_clock::time_point
  17. How can I use Standard Library (STL) classes in my dll interface or ABI?
  18. Passing rvalues through std::bind
  19. How to truncate a file while it is open with fstream
  20. cc1plus: error: unrecognized command line option “-std=c++11” with g++
  21. std::lexical_cast – is there such a thing?
  22. Does clearing a vector affect its capacity?
  23. std::forward_list and std::forward_list::push_back
  24. Sorting a vector of objects by a property of the object
  25. Can a declaration affect the std namespace?
  26. Why does unique_ptr take two template parameters when shared_ptr only takes one?
  27. Element at index in a std::set?
  28. What’s the time complexity of iterating through a std::set/std::map?
  29. What data structure is inside std::map in C++?
  30. How to make sure that std::random_shuffle always produces a different result?

Leave a Comment